Welcome to the first io9 music smackdown! We're putting together the ultimate science fiction (and fantasy) playlist — all the music that everyone should have on his or her iPod.

Today, help us decide which theme tunes absolutely must be in the mix. Which would you rather have in your ultimate science fiction playlist: the theme from Firefly or BSG?

Here are the rules for this particular playlist. Only original TV theme songs are eligible (so Chuck's Cake tune and True Blood's "Bad Things" are out, but just for this round). There are no cartoons for this round as well, you'll get your TMNT cartoon theme song smack down soon enough. You can vote for 4 total. The winners will be added to io9's ultimate play list. The poll is at the bottom of the posts, and we've included every single song on the list so you can decide first-hand.